Abstract

Albitization of K-feldspar has been studied experimentally at 500 and 750 °C and 200 MPa using concentrated NaCl solutions. The partially reacted feldspar grains were characterized using X-ray diffraction, electron probe microanalysis, transmission electron microscopy as well as Raman and laser-induced photoluminescence spectroscopy. The replacement of K-feldspar by albite occurs via coupled dissolution-reprecipitation due to the mobilization of K in exchange for Na and results in the mobilization of minor elements like Ba, Fe, Ti, and Mg. The release of tetrahedrally incorporated Fe3+ and Ti4+ in K-feldspar is temperature-dependent resulting in increasing mobilization with increasing temperature. Barium shows a positive correlation with K in the reacted areas. Replacement also leads to the formation of cogenetic rutile and Fe-rich pseudobrookite inclusions in the albitized regions. This supports the proposal that the Fe responsible for the formation of hematite inclusions in altered, natural alkali feldspars can originate from the feldspar.